Glossary

A

artifact

A visual imperfection in an encoded video clip. Too many artifacts can make the video look blocky.

B

bandwidth

The upper limit on the amount of data, typically expressed as Kilobits per second (Kbps), that can pass through a network connection.

binary tag

An XML tag that comprises opening and closing tags, such as <List> and </List>.

bit

The smallest unit of measure of data in a computer. A bit has a binary value, either 0 or 1.

bit rate

A measure of bandwidth, expressed as the number of bits transmitted per second. A 28.8 Kbps modem, for example, can transmit or receive around 29,000 bits per second.

broadcast

To deliver a presentation, whether live or prerecorded, in which all viewers join the presentation in progress. Contrast to on-demand.

buffering

The receiving and storing of data before it is played back. A clip's initial buffering is called preroll. After this preroll, excessive buffering may stall the presentation.

byte

A common measurement of data. One byte consists of 8 bits.

C

cable modems

Devices that allow rapid transmission and reception of data over television cable. They are digital devices, unlike dial-up modems, which transmit analog data.

CBR

Constant Bit Rate. A type of RealVideo encoding in which all parts of the video play back at the same bit rate. Contrast to VBR.

client

A software application that receives data from a server. A Web browser is a client of a Web server. RealPlayer is a client of Helix Server.

clip

A media file within a presentation. Clips typically have an internal timeline, as with RealAudio and RealVideo.

codec

Coder/decoder. Codecs convert data between uncompressed and compressed formats, reducing the bandwidth a clip consumes.

D

download

To send a file over a network with a nonstreaming protocol such as HTTP. Contrast to stream.

DSL

Digital Subscriber Line. A technology for transmitting digital data over a regular telephone line much faster than through dial-up modems.

duress stream

A low-bandwidth SureStream audio or video stream that Helix Server uses if a connection's available bandwidth drops greatly.

E

encoding

Converting a file into a compressed, streaming format. For example, you can encode WAV files as RealAudio clips.

F

fps

Frames Per Second. The number of video frames that displays each second in a streaming video clip.

frequency response

A measure of audio clip quality. The higher a clip's frequency response, the more frequencies it can faithfully reproduce.

H

Helix Server

RealNetworks server software used to stream multimedia presentations to RealPlayer 10.

Helix Server administrator

The person in charge of setting up and running Helix Server.

HTTP

Hypertext Transport Protocol. The protocol used by Web servers to communicate with Web browsers. In contrast, Helix Server streams clips to RealPlayer with RTSP.

I

ISDN

Integrated Services Digital Network. Technology that makes digital data connections at 64 or 112 Kbps possible over telephone lines.

ISP

Internet Service Provider. A company that provides access to the Internet. Many ISPs have Helix Server available to stream media clips.

K

kilobit (Kb)

A common unit of data measurement equal to 1024 bits. A kilobit is usually referred to in the context of bit rate per unit of time, such as Kilobits per second (Kbps).

kilobyte (KB)

A common unit of data measurement equal to 1024 bytes or 8 Kilobits.

L

LAN

Local Area Network. A computer network confined to a local area, such as a single building. LANs vary in speed, with bandwidth shared among all networked devices.

lossy

A compression scheme that lowers clip size by discarding nonessential data from the source file. Both RealAudio and RealVideo are lossy.

M

metafile

Another name for a Ram file.

mouseover

The action of moving a computer screen pointer over an interactive area. An animated button may change appearance on a mouseover, for example.

N

namespace

An XML declaration that identifies the features used in a SMIL presentation. For SMIL 2.0 and higher, the <smil> tag must declare a namespace.

O

on-demand

A type of streaming in which a clip plays from start to finish when a user clicks a link. Most clips are streamed this way. Contrast to broadcast.

P

PNA

A proprietary protocol Helix Server uses for backward compatibility with RealPlayer 3 through 5. URLs using PNA start with pnm://.

port

A connection to a server, designated by a number such as 8080. Helix Server uses different ports for the RTSP, HTTP, and PNA protocols.

preroll

Buffering that occurs just before a clip plays back. Preroll should be no more than 15 seconds.

presentation

A group of clips coordinated through SMIL and streamed from Helix Server to RealPlayer 10.

R

Ram file

A text file that uses the file extension .ram or .rpm. It launches RealPlayer and gives it the URL to a streaming clip or presentation.

RDT

RealNetworks Data Transport. The proprietary data package Helix Server uses (along with RTSP) when communicating with RealPlayer. Contrast to RTP.

RealAudio

A clip type for streaming audio over a network. RealAudio clips use the .rm extension.

RealPlayer 10

The successor to RealOne Player, RealPlayer 10 combines streaming and digital download technologies.

RealPix

A clip type (file extension .rp) for streaming still images over a network. RealPix uses a markup language for creating special effects such as fades and zooms.

RealPlayer G2

The RealNetworks client software that introduced plug-ins and the ability to update itself. It, along with the later RealPlayer 7 and RealPlayer 8, supports the SMIL 1.0 standard.

RealProducer

The primary RealNetworks tool for encoding RealAudio and RealVideo clips.

RealText

A clip type (file extension .rt) for streaming text over a network. It uses a markup language for formatting text.

real-time

Delivered as it occurs. For example, a live event is streamed across a network in a real-time broadcast.

RealVideo

A clip type for streaming video over a network. RealVideo clips use the extension .rm.

rebuffering

An undesirable state in which RealPlayer must pause a presentation to wait for streaming data to arrive. Rebuffering can result from network conditions, or a poorly produced presentation.

RTP

Real-Time Transport Protocol. The open, standards-based data package Helix Server uses (along with RTSP) to communicate with RTP-based clients. Contrast to RDT.

RTSP

Real-Time Streaming Protocol. An open, standards-based control protocol that Helix Server uses to stream clips to RealPlayer or any RTP-based client. Contrast to HTTP.

S

server

1. A software application, such as a Web server or Helix Server, that sends requested data over a network.

2. A computer that runs server software.

SMIL

Synchronized Multimedia Integration Language. A markup language for specifying how and when each clip plays within a presentation. SMIL files use the extension .smil.

stream

1. To send a media clip over a network so that it begins playing back as quickly as possible.

2. A flow of a single type of data, measured in Kilobits per second (Kbps). A RealVideo clip's soundtrack is one stream, for example.

SureStream

A RealNetworks technology that enables a RealAudio or RealVideo clip to stream at multiple bit rates.

U

unary tag

An XML tag that includes a closing slash, as in <ref/>.

URL

Uniform Resource Locator. A location description that enables a Web browser or RealPlayer to receive a clip stored on a Web server or Helix Server.

V

VBR

Variable Bit Rate. A type of RealVideo encoding that enables RealPlayer to play different parts of the video at different bit rates, even though the video is streamed at a constant rate. Contrast to CBR.

X

XML

Extensible Markup Language. The parent language for SMIL. XML allows one to develop flexible, standardized languages for any purpose.

©2004 RealNetworks, Inc. For more information, visit RealNetworks Click here if the Table of Contents frame is not visible at the left side of your screen.